Diel patterns of UVBR-induced DNA damage in picoplankton size fractions from the Gulf of Aqaba,Red Sea |
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Authors: | Boelen P Post A F Veldhuis M J W Buma A G J |
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Institution: | (1) Department of Marine Biology, Centre for Ecological and Evolutionary Studies, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands, NL;(2) H. Steinitz Marine Biology Laboratory, The Interuniversity Institute for Marine Science, PO Box 469, 88103 Eilat, Israel, IL;(3) Department of Biological Oceanography, Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands, NL |
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Abstract: | This study focuses on the impact of natural levels of UVBR (ultraviolet-B radiation: 280 to 315 nm) on bacterio- and phytoplankton
(<10 mm) from the Gulf of Aqaba, Red Sea. Incident biologically effective doses (BEDs) and attenuation of biologically effective
radiation in the water column were measured using a DNA biodosimeter. UVBR-induced DNA damage was measured as cyclobutane
pyrimidine dimers (CPDs), using an antibody directed to CPDs followed by chemiluminescent detection. Depth profiles of DNA
damage were determined in two plankton size fractions (0.2 to 0.8 mm and 0.8 to 10 mm) collected down to 50 m depth. Furthermore,
accumulation and removal of CPDs were monitored in surface plankton samples during several daily cycles. Small plankton (plankton
<10 mm) composition was determined by flow cytometry. The plankton community in the Gulf of Aqaba was dominated by nonphototrophic
bacteria and the free-living prochlorophyte Prochlorococcus spp. (<0.8 mm). In general, no DNA damage could be detected in
dosimeter DNA below 15 m. In contrast, DNA damage (up to 124 CPD Mnucl-1) could be detected in all bacterio- and phytoplankton
samples. DNA damage accumulated throughout the day, indicating that plankton in the Gulf of Aqaba undergo UVBR stress via
CPD induction. Although the numbers of CPDs decreased during darkness, both size fractions showed some residual DNA damage
at the end of the night. This suggests that dark repair processes did not remove all CPDs, or that part of the plankton community
was incapable of repair at all. CPD levels in the two size fractions showed no significant differences in situ. During full
solar radiation exposures (samples incubated in bags), more CPDs were detected in the smaller (0.2 to 0.8 mm) size fraction
as compared to the larger (0.8 to 10 mm) size fraction. In these experiments, initial plankton composition was significantly
different from the field samples. This implies that a shift in the population structure or irradiance conditions can lead
to a significant change in UVBR sensitivity. In conclusion, the results show that the picoplankton-dominated phyto- and bacterioplankton
communities in the clear surface waters from the Gulf of Aqaba undergo UVBR stress. Repair pathways are not sufficient to
eliminate damage during or after UVBR exposure hours, suggesting photomortality as a potential loss parameter of the plankton
community. |
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